1. Field of the Invention
This invention relates in general to a method of purifying an organometallic compound, and more particularly to a method of purification to reduce impurities contained in an organometallic compound which is useful as a material used in epitaxial growth by MOCVD (Metal Organic Chemical Vapor Deposition) for manufacturing compound semiconductors.
2. The Prior Art
Recently, use of compound semiconductors of the III-V group and II-VI group has begun in a wide variety of applications such as semiconductor light emitting elements and microwave transistors, and because of their superior characteristics these semiconductors are now used in integrated circuits for high speed computers, integrated circuits for optoelectronics, etc.
The compound semiconductors used in this wide range of applications are manufactured with the MOCVD method using an organometallic compound for the crystal growth method. The MOCVD method is one of crystal growth methods which are frequently used when forming an epitaxial thin film of a compound semiconductor or a mixed crystal semiconductor. It uses an organometallic compound such as trimethyl indium, trimethyl gallium or dimethyl zinc and utilizes their heat decomposition reaction for crystal growth of a thin film.
The characteristics of compound semiconductors formed by the epitaxial growth of an organometallic compound are considerably dependent on the purity of the organometallic compound, and impurities have substantial adverse effects on electrical characteristics and optical characteristics. Therefore, it is necessary to use a highly purified organometallic compound. To meet this requirement, purification distillation has been carried out with a conventional distillation operation. However, the conventional distillation operation alone cannot provide an organometallic compound with sufficiently high purity.
In order to solve this problem, a method in which the organometallic compound containing impurities was exposed to activated charcoal (Japanese examined patent publication Tokko Hei 6-39477) and a method employing a reducing agent such as a metal hydride compound (Tokko Hei 5-29371) were tried.
However, they are not advantageous in a practical sense if used for an organometallic compound which is solid at normal temperatures such as trimethyl indium although these methods are effective for an organometallic compound which is liquid at normal temperatures. This is because most of the distiller or the facility has to be maintained at the melting point of the organometallic compound or higher, the distiller or the facility is complex and the treatment operation is complicated.